1. Field of the Invention
The present invention relates to an image forming apparatus in which sheets are discharged into any one of a plurality of sheet stacking means.
2. Description of the Related Art
There has been proposed a discharging option for a printer in which movable discharging bins have only one sensor for detecting the amount of paper stacked in each discharging bin and the detection is performed by moving each discharging bin. In addition, a method of controlling a printer connected to the discharging option has been proposed. In this control method, a print instruction is received from a host computer and command analyzing is performed. The determination whether to start printing is based on previously-obtained discharging-bin information rather than on the present state of the discharging bin.
The above-described conventional examples have the following problems:
In the printer, only while actual feeding and discharging is being performed can the condition of the discharging bin in use be detected. If the discharging bin is already full when the print instruction is received, several sheets are still printed because the detection of the stacked-paper amount is performed during actual discharging. Accordingly, several sheets are discharged into the fully-stacked discharging bin before notification of the full stack is issued. In other words, if the discharging bin is changed by a discharging-bin selecting instruction transmitted as part of print data from the host computer, the stacked-paper amount in the selected discharging bin cannot be detected until the previous sheets are discharged by performing the next printing because a discharging bin into which the previous discharging was performed had been operational (in a condition capable of detecting the stacked-paper amount). Accordingly, the processing must be performed based on the previous information. In the case of a discharging system with one single sensor that can detect only the stacked-paper amount in the operational discharging bin, detection is impossible when a user removes paper from or puts paper in a discharging bin other than the operational discharging bin. The system cannot operate based on accurate information because only the stacked-paper amount in the operational discharging bin to a newly can be detected.
As described above, only after discharging is started can an accurate stacked-paper amount be detected. Thus, a discharging bin that is already full may be used as the selected discharging bin. Thus, sheets are discharged into the fully-stacked discharging bin, and paper jamming occurs in the discharging system, which often causes malfunctioning.
In the case where paper in the fully-stacked discharging bin, which is not operational, is removed by the user, a problem occurs in that the discharging system has determined that the bin is fully-stacked, and prohibits the discharging bin from being used despite the fact that paper can be practically stacked in the discharging bin.
In the case where the discharging system has two modes: an automatic discharging mode for discharging into an empty discharging bin, and a fixed discharging mode for discharging into one fixed discharging bin, the modes may be mixed when being used by a plurality of users in a network environment. If, in the automatic discharging mode, a user performs a job that needs discharging a large amount of paper, the paper may be discharged into a plurality of discharging bins. By way of example, in the case where a user A performs fixed outputting to a second discharging bin, and another user B uses the automatic discharging mode to perform a large-amount of outputting to a first discharging bin as a starting point, the output of user B is discharged into the second discharging bin after the first discharging bin is full. Thus, the output of user B is stacked on the output of user A. The output of user A is mixed in the output of user B. Therefore, user B, who does not know that the output of user A has been discharged into the second discharging bin, may mistakenly remove the output of user A.
Accordingly, it is an object of the present invention to provide an image forming apparatus in which the foregoing problems are solved.
To this end, according to an aspect of the present invention, the foregoing object has been achieved through provision of an image forming apparatus comprising: image forming means for forming images on sheets; a plurality of sheet stacking means in which the sheets are stacked; selector means for selecting one sheet stacking means; moving means for moving to a predetermined position the selected sheet stacking means; detection means for detecting the sheet-stacked condition of the selected sheet stacking means; and control means for performing control so that, when the selected sheet stacking means is changed to a newly selected sheet stacking means, the moving means moves the newly selected sheet stacking means to the predetermined portion, and after the detection means detects the sheet-stacked condition of the newly selected sheet stacking means, image formation by the image forming means is started.
According to another aspect of the present invention, the foregoing object has been achieved through provision of an image forming apparatus comprising: image forming means for forming images on sheets; a plurality of sheet stacking means for stacking the sheets; control means for activating a first mode in which the sheets are stacked by the sheet stacking means selected by an external unit, and a second mode in which the sheets are stacked by the sheet stacking means automatically selected by the image forming apparatus; and information means used such that, in the second mode, when the selected sheet stacking means is changed to a newly selected sheet stacking means, the information means gives information urging sheet removal depending on the sheet-stacked condition of the newly selected sheet stacking means.
According to a further aspect of the present invention, the foregoing object has been achieved through provision of a stacker comprising: stacking means for stacking sheets on which images are formed; discharging control means for performing either of face-down discharging and face-up discharging onto the stacking means; detection means for detecting the amount of the sheets stacked on the stacking means; and full-stack detecting means for detecting whether there is a full stack of the sheets on the stacking means by determining whether the detected amount of said sheets at least equals a first predetermined amount when face-down discharging is performed by the discharging control means, and a second predetermined amount, which is less than the first predetermined amount when face-up discharging is performed by the discharging control means.